Wireless communication systems are well known in the art. Generally, such systems comprise communication stations, which transmit and receive wireless communication signals between each other. Depending upon the type of system, communication stations typically are one of two types of wireless transmit/receive units (WTRUs): one type is the base station, the other is the subscriber unit, which may be mobile.
The term base station as used herein includes, but is not limited to, a base station, access point (AP), Node B, site controller, or other interfacing device in a wireless environment that provides other WTRUs with wireless access to a network with which the base station is associated.
The term subscriber unit as used herein includes, but is not limited to, a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. Such WTRUs include personal communication devices, such as phones, video phones, and Internet ready phones that have network connections. In addition, WTRUs include portable personal computing devices, such as PDAs and notebook computers with wireless modems that have similar network capabilities. WTRUs that are portable or can otherwise change location are referred to as mobile units.
Typically, a network of base stations is provided wherein each base station is capable of conducting concurrent wireless communications with appropriately configured WTRUs, as well as multiple appropriately configured base stations. Some WTRUs may alternatively be configured to conduct wireless communications directly between each other, i.e., without being relayed through a network via a base station. This is commonly called peer-to-peer wireless communications. Where a WTRU is configured to communicate directly with other WTRUs it may itself also be configured as and function as a base station. WTRUs can be configured for use in multiple networks, with both network and peer-to-peer communications capabilities.
One type of wireless system, called a wireless local area network (WLAN), can be configured to conduct wireless communications with WTRUs equipped with WLAN modems that are also able to conduct peer-to-peer communications with similarly equipped WTRUs. Currently, WLAN modems are being integrated into many traditional communicating and computing devices by manufacturers. For example, cellular phones, personal digital assistants, and laptop computers are being built with one or more WLAN modems.
In the wireless cellular telephone context, one current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). General Packet Radio Service (GPRS) and Enhanced Data for GSM Evolution (EDGE) are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard. In addition to the 3GPP standards, 3GPP2 standards are being developed that use Mobile IP in a Core Network for mobility.
Popular WLAN environments with one or more WLAN base stations, typically called access points (APs), are built according to the IEEE 802 family of standards. Access to these networks usually requires user authentication procedures. Protocols for such systems are presently being standardized in the WLAN technology area such as the framework of protocols provided in the IEEE 802 family of standards.
A basic service set (BSS) is the basic building block of an IEEE 802.11 WLAN, which comprises WTRUs also referred to as stations (STAs). Basically, the set of STAs which can talk to each other can form a BSS. Multiple BSSs are interconnected through an architectural component called a distribution system (DS), to form an extended service set (ESS). An access point (AP) is a WTRU that provides access to the DS by providing DS services, and generally allows concurrent access to the DS by multiple STAs.
In an AP-based WLAN, a WTRU must communicate wirelessly with a specific AP situated in its vicinity. The WTRU is said to be associated with this AP. It is sometimes necessary or desirable for a WTRU to change the AP to which it is associated (“reassociation”). For example, the WTRU may be experiencing poor signal conditions because it is moving out of the geographic area served by the AP with which it is originally associated (original AP). Poor signal conditions can also be caused by congestion arising in the basic service set (BSS) served by the original AP.
A WTRU can use a WLAN to communicate via the Internet by establishing a communication session with an Internet server via the associated AP, and obtaining a unique IP address. Generally this type of communication requires establishing routing information that allows the WTRU to send information to the Internet and to receive information sent to its IP address from the Internet. Maintaining the communication session when the WTRU reassociates to a new AP requires a mechanism to transfer the session to the new AP and update the routing information.
A WTRU can also be configured to communicate with two or more different types of networks. Such a device is called a multimode WTRU. For example, a WTRU may be configured to communicate with three different networks such as an 802.11 (WiFi) network, an 803.16 (WiMAX) network and a cellular telephone network. Multimode WTRUs can be configured to operate independently in each type of network in which it they are configured to operate. For example, a multi-mode WTRU is disclosed in U.S. Publication No. 20040248615 published Dec. 9, 2004 and owned by the assignee of the present invention.
In an independent multimode implementation, the WTRU may conduct one or more communications under different communication standards, but can only handover a particular communication within the context of the same type of network. In order to provide additional functionality and versatility, it is desirable to provide a handover mechanism which allows a multimode WTRU to handover a communication from one type of network station using one communication standard to another type of network station using a different communication standard.